"When we add up the heat loss from a home we need to be sure we are only counting those BTUs once.

How often have you heard the statement that air leakage reduces the effectiveness of the insulation? It's one of those things that's easy to see. Turn on the blower door on a cold day and watch the cold areas grow as the infiltration chills the walls. We are even supposed to look at the resulting patterns and reduce the grade of the insulation accordingly. Well, would you be surprised to learn that infiltration and exfiltration do not degrade the performance of the insulation when that air passes through? If it is r-19 with no air passing through, it is still r-19 with the leaks.

Here's where the distinction comes in. If the infiltration on a cold day was headed all the way into the house, it was going to get warmed up to room temperature at some point anyway and those BTUs will be accounted for when dealing with the somehow determined air leakage number. To further degrade the wall assembly insulation value would be penalizing that home twice for the same heat loss.

There are examples like attic venting where incoming air blows through the insulation and then carries that stolen heat out the high vents, but since no other calculation is accounting for that loss, then degrading the insulation is probably appropriate."

This is truly shooting from the hip as even I have concerns about my explanation. Any help appreciated.

Replies to This Discussion

"Air conditioning" to me is really antiquated for desert living where wind-solar can provide the cold and thermal-fluids are how to move it to rooms, not air, this about 10-times more thermally efficient moving the fluid, then pumping the fluid takes less power than the blowers moving the air.

That implies a lot of room for improvement, what's hard about a small windmill driving the compressor for freon instead of electricity when it's available? Propane refrigeration uses heat as do most ice-houses to make the cold and why aren't solar dishes used then as well, backed up by a common fuel or laser?

With alternatives you pay for capacity and storage is always brought up so when using thermal fluids there is an easy way to do that with insulated tanks to store enough for on-demand use for a daily cycle. I lived in a 1917 home in Phoenix, AZ, that was 160F in the attic with the swamp cooler driving the air conditioner up there and cost over $350/month to keep the place at 80F at night due mainly to a brick wall facing the setting sun having no late afternoon shade thus using thermal mass exactly the wrong way!

Perfect example and modern homes aren't much better, they plug-n-play and you pay, there's no reason for landlords or the energy industry to change it the point, they don't live there and both profit from status-quo.

There are masterworks of adobe in the Southwest, when you walk in it's cool in summer and warm in winter and these prove a mastery of observed ways to control gain and storage of heat and cold by the adobe along with the wall placements & thickness, and, they raised and lowered floor levels as well. Those to our plug-n-play society may be worth exact study to establish the principles better for computer models to replicate their traditional science for us.

Agree with Bud's point that infiltration is getting input to the equation twice so results won't be correct.

Your point "more things to consider" is a broad topic that varies all across this country and one that makes "in and out" audits difficult. What works for one area my be bad for another. I'm in Maine and our outside air is fairly good as long as you don't live near a paper mill (most have improved). But I have traveled some of the Cal coast and I can't imagine wanting that fog to filter through my attic.

A point on the "dust from vented attics", besides going to a sealed attic, shifting the balance of high and low vent area to favor the high will move the neutral plane up and increase the negative pressure at the attic floor. In a heating climate that is not desirable, but in a cooling dominated climate, this 'more negative' pressure counters the negative stack effect from the cool house and tends to reduce the attic to house infiltration. Just another consideration to add to the list.